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The Iosif Stalin tank (or IS tank, named after the Soviet leader Joseph Stalin), was a heavy tank developed by the Soviet Union during World War II. The tanks in the series are also sometimes called JS or ИС tanks.

The heavy tank was designed with thick armour to counter the German 88 mm guns, and sported a main gun that was capable of defeating the German Tiger and Panther tanks. It was mainly a breakthrough tank, firing a heavy high-explosive shell that was useful against entrenchments and bunkers. The IS-2 was put into service in April 1944, and was used as a spearhead in the Battle of Berlin by the Red Army in the final stage of the war.
Design and production
[edit] IS-1

The KV series of Soviet heavy tanks was criticized by their crews for their low mobility, and lack of any heavier armament than the T-34 medium tank. In 1942, this problem was partially addressed by the lighter, faster KV-1S tank. The KV series remained much more expensive than the T-34, without having greater combat performance. The heavy tank program was nearly cancelled by Stalin in 1943. However, the German employment of substantial numbers of Panther and Tiger tanks at the Battle of Kursk in the summer of 1943 changed Soviet priorities. In response, the Soviet tank industry created the stopgap KV-85, and embarked on the KV-13 design program to create a tank with more advanced armour layout and a more powerful main gun. Because Marshal Kliment Voroshilov had fallen out of political favour, the new heavy tank series was named Iosif Stalin tank. The IS-85 prototype was initially accepted for production as the IS-1 heavy tank.
[edit] IS-2

Gun choice

Two candidate weapons were the A-19 122 mm gun and the BS-3 100 mm gun. The BS-3 (later adopted on the SU-100 tank destroyer and the T-55 tank) had superior armour penetration (185 mm compared to 160 mm), but a less useful high explosive round. Also, the BS-3 was a relatively new weapon in short supply. Excess production capacity existed for the A-19 and its ammunition. Compared to the older 76.2 mm tank gun, the A-19 had very good armour penetration, similar to that of the effective 75 mm high velocity gun mounted on the German Panther, and delivered 3.5 times the kinetic energy of the older F-34.

After testing with both BS-3 and A-19 guns, the latter was selected as the main armament of the new tank, primarily because of its ready availability and the effect of its large high-explosive shell when attacking German fortifications. The A-19 used a separate shell and powder charge, resulting in a lower rate of fire and reduced ammunition capacity, both serious disadvantages in tank-to-tank engagements. However, the gun was very powerful, and while its 122 mm armour piercing shell had a lower muzzle velocity than similar late-issue German 75 mm and 88 mm guns, Soviet proving-ground tests established that the A-19 could penetrate the front armour of the German Panther tank [2], and it was therefore considered adequate in the anti-tank role.

German Army data on the penetration ranges of the 122 mm A-19 gun against the Panther tank showed it to be much less effective than the Soviets thought: the A-19 gun was unable to penetrate the glacis plate of the Panther at any distance, and could only penetrate the bottom front plate of the hull at 100 m.[3] It was however the large HE shell the gun fired which was its main asset, proving highly useful and destructive in the anti-personnel role. The size of its gun continued to plague the IS-2, the two-piece ammunition was difficult to manhandle and very slow to reload (the rate of fire was only about two rounds per minute). Another limitation imposed by the size of its ammunition was the payload: a mere 28 rounds could to be carried inside the tank. [4]

IS-2 Production

The IS-122 prototype replaced the IS-85, and began mass production as the IS-2. The 85 mm guns could be reserved for the new T-34-85 medium tank, and some of the IS-1s built were rearmed before leaving the factory, and issued as IS-2s.

The main production model was the IS-2, with the powerful A-19. It was slightly lighter and faster than the heaviest KV model 1942 tank, with thicker front armour and a much-improved turret design. The tank could carry thicker armour than the KV series, while remaining lighter, due to the better layout of the armour envelope. The KV’s armour was less well-shaped and featured heavy armour even on the rear, while the IS series concentrated its armour up front. The IS-2 weighed about the same as a German Panther and was lighter than the German heavy tank Tiger series. It was slightly lower than both.

While the design was good for its time, Western observers[who?] tended to criticize Soviet tanks for their lack of finish and crude construction. The Soviets responded that it was warranted considering the need for wartime expediency and the typically low battlefield life of their tanks[5].

Early IS-2s can be identified by the ‘stepped’ front hull casting with its small, opening driver’s visor. The early tanks lacked gun tube travel locks or antiaircraft machine guns, and had narrow mantlets.

Later improved IS-2s (the model 1944), had a faster-loading version of the gun, the D25-T with a double-baffle muzzle brake and better fire-control. It also featured a simpler hull front without a ‘step’ in it (using a flat, sloping glacis armour plate). Some sources called it IS-2m, but it is not to be confused with the official Soviet designation IS-2M for a 1950s modernization. Other minor upgrades included the addition of a travel lock on the hull rear, wider mantlet, and, on very late models, an antiaircraft machine gun.
IS-3
In late 1944 the design was upgraded to the IS-3. This tank had improved armour layout, and a hemispherical cast turret (resembling an overturned "soup bowl") which became the hallmark of post-war Soviet tanks. While this low, hemispherical turret may have made the IS-3 a smaller target, it also imposed severe penalties inside the tank by significantly diminishing the working headroom, especially for the loader (Soviet tanks in general are characterized by uncomfortably small interior space compared to Western tanks). The low turret also limited the maximum depression of the main gun, since the gun breech had little room inside the turret to pivot on its vertical axis. As a result, the IS-3 was less able to take advantage of hull-down positions, a tactic at which Western tanks were better suited[6]. The IS-3’s pointed prow earned it the nickname Shchuka (Pike) by its crews. It weighed slightly less and stood 30 cm lower.

The IS-3 came too late to see action in World War II. Though some older sources claim that the tank saw action at the end of the war in Europe, there are no official reports to confirm this. It is now generally accepted that the tank saw no action against the Germans, although one regiment may have been deployed against the Japanese in Manchuria.

In 1952, a further development was put into production, the IS-10. Due of the political climate in the wake of Stalin’s 1953 death, it was renamed T-10.

In the mid-1950s, the remaining IS-2 tanks (mostly model 1944 variants) were upgraded to keep them battle-worthy. This upgrade produced the IS-2M, which introduced fittings such as external fuel tanks on the rear hull (the basic IS-2 had these only on the hull sides), stowage bins on both sides of the hull, and protective skirting along the top edges of the tracks. IS-3 was also slightly modernized as IS-3M.

Operational history

The IS-2 tank first saw combat in the spring of 1944. IS-2s were assigned to separate heavy tank regiments, normally of 21 tanks each.[7] These regiments were used to reinforce the most important attack sectors during major offensive operations. Tactically, they were employed as breakthrough tanks. Their role was to support infantry in the assault, using their large guns to destroy bunkers, buildings, dug-in crew-served weapons, and other ‘soft’ targets. They were also capable of taking on any German AFVs if required. Once a breakthrough was achieved, lighter, more mobile T-34s would take over the exploitation.

The IS-3 first appeared to Western observers at the Allied Victory Parade in Berlin in September 1945. The IS-3 was an impressive development in the eyes of Western military observers, the British in particular, who responded with heavy tank designs of their own.

By the 1950s, the emergence of the main battle tank concept – combining medium tank mobility with the firepower of the heavy tank – had rendered heavy tanks obsolete in Soviet operational doctrine. In the late 1960s, the remaining Soviet heavy tanks were transferred to Red Army reserve service and storage. The IS-2 Model 1944 remained in active service much longer in the armies of Cuba, China and North Korea. A regiment of Chinese IS-2s was available for use in the Korean War, but saw no service there. In response to border disputes between the Soviet Union and China, some Soviet IS-3s were dug in as fixed pillboxes along the Soviet-Chinese border. The IS-3 was used in the 1956 Soviet invasion of Hungary and the Prague Spring in 1968.

During the early 1950s all IS-3s were modernised as IS-3M models. The Egyptian Army acquired about 100 IS-3M tanks in all from the Soviet Union.[8] During the Six Day War, a single regiment of IS-3M tanks was stationed with the 7th Infantry Division at Rafah and the 125th Tank Brigade of the 6th Mechanized Division at Kuntilla was also equipped with about 60 IS-3M tanks.[9] Israeli infantry and paratrooper units had considerable difficulty with the IS-3M when it was encountered due to its thick armour, which shrugged off hits from normal infantry anti-tank weapons such as the bazooka.[9] Even the 90mm AP shell fired by the main gun of the Israeli Defense Force (IDF) M-48A2 Patton tanks could not penetrate the frontal armour of the IS-3s at normal battle ranges.[9] There were a number of engagements between the M48A2 Pattons of the IDF 7th Armoured Brigade and IS-3s supporting Egyptian positions at Rafah in which several M48A2s were knocked out in the fighting.[9] Despite this, the slow rate of fire, poor engine performance (the engine was not well suited to hot-climate operations), and rudimentary fire control of the IS-3s proved to be a significant handicap, and about 73 IS-3s were lost in the 1967 war.[9] Most Egyptian IS-3 tanks were withdrawn from service, though at least one regiment of IS-3 tanks was retained in service as late as the 1973 October war.[9] The IDF itself experimented with a few captured IS-3M tanks, but found them ill-suited to fast moving desert tank warfare; those that were not scrapped were turned into stationary defensive pillbox emplacements in the Jordan River area.[9]

After the Korean War, China attempted to reverse-engineer the IS-2/IS-3 as Type 122 medium tank.[10] The project was cancelled in favour of the Type 59, a copy of the Soviet T-54A.